The invention relates to compounds falling within the following structure (I): EQU (R.sub.1).sub.a (R.sub.2).sub.b SiX.sub.c (I)
wherein R.sub.1 is a neophyl, neohexyl or (CH.sub.3).sub.3 SiCH.sub.2 --group; R.sub.2 is a methyl group; X is a halo group or a saturated, unsaturated, branched, unbranched or cyclic alkoxy group of 1-18 carbon atoms; a is 1 or 2, b is an integer from 0 to 2, and c is an integer from 1 to 3. The neophyl group is a 2-phenyl-2-methylpropyl group, and the neohexyl group is a 3,3-dimethylbutyl group. The X group represents the functionality of the compounds of the invention. Thus, the compounds of the invention include mono- and polyfunctional silanes.
Sterically-hindered organosilanes have been synthesized by a variety of methods, including hydrosilation of sterically-hindered olefins, reaction of organolithium reagents or organomagnesium halides with halo or alkoxysilanes, and by rearrangements of suitably substituted vinylsilanes.
Monofunctional silanes, including halo- or alkoxysilanes, are often used to generate support structures for use in liquid chromatography. The support structures are prepared by coating the surface of a substrate with sterically-hindered silanes, such as the compounds of the present invention. The substrates already include hydrolyzed silica or chromia which have on their surface hydroxyl groups available for reaction with the sterically-protecting silane reagent. The monofunctional silanes form trialkylsilyl ethers on the surface of the substrate. The chromatographic characteristics are generally imparted by the bulky substituent, such as R.sub.1 in structure (I).
Such substrates can be generated with polyfunctional silanes as well. When polyfunctional silanes are employed, the silanes generally polymerize with each other along the surface of the substrate in addition to reacting with the substrate, leaving a surface layer which may not be as well-defined as a layer generated from monofunctional silanes. Both types of structures can be useful media for chromatographic separations. The use of polyfunctional silanes can generate support structures with increased resistance against hydrolysis. Silane support structures, generated from compounds such as those of the present invention, can have unique stabilities to hydrogenolytic or organometallic reagents, reducing agents, and basic or acidic reagents. The structures can often be useful as high performance liquid chromatography packings for separating a wide variety of macromolecules, allowing reproducible analysis of mixtures or isolation of purified components.
It is also known that alkoxysilanes, such as those contemplated by structure (I) wherein X is an alkoxy group, can be used as external electron donors in supported Ziegler-Natta catalysts. In J. V. Seppala, M. Harkonen, "Effect of the Structure of External Alkoxysilane Donors on the Polymerization of Propene with High Activity Ziegler-Natta Catalysts", Makromol Chem. 190, 2535-2550 (1989), the authors suggest that in the context of propene polymerization, high performance external donors should have two or three alkoxy groups and relatively large, non-linear hydrocarbon groups. The authors also conclude that effective external donors should not have alkoxy substituents that are larger than the ethoxy group, as with the preferred alkoxy compounds of the present invention.
Sterically-hindered organosilanes, such as those of the present invention, can also be useful as blocking agents for organic synthesis.